Leather manufacturing



Patented May 26, 1936 g UNITED STATES PATENT OFFICE 2,041,732 LEATHERMANUFACTURING No Drawing. Application July 7, 1934,

Serial No. 734,193

5 Claims.

The present invention relates to improvements in leather manufacture andit particularly relates to an improvement in the dehairing and unhairingof skins and hides.

5 Considerable dimculty has been encountered in satisfactorily employingenzymes, particularly of proteolytic-nature, in commercial processes fordehairing and/or bating skins and hides. In the .various processesinvolved in the manufacture of 10 leather, and particularly in thedehairing and bating processes, the various steps and processes areclosely inter-related and it is necessary at all times to carefullyadjust each step and operation in relation to each other step andoperation,

15 as otherwise the skin or hide will not be satisfactorily. treated norwill it be converted into a most desirable grade of leather.

In dehairing with enzyme preparations it has been found desirable totreat the skin or hide with 20 a relatively strong alkali, as causticsoda, sodium sulphide and other strong alkalies, to cause properswellingthereof. It was usually customary, subsequent to the alkaliswelling process, to neutralize skin or hide, as for example, withsodium bi- 25 carbonate until a relatively low pH, slightly above theneutral point was obtained, as for example, at a pH of about 7 to 8. Atthis relatively low pH the hide or skin was treated with the enzymepreparation which preferably would not be disiO advantageously affectedif the leather were maintained at relatively low pH values just on thealkaline side of neutrality.

To give one example of the prior art practices it was customary toreduce the alkalinity of the i5 hides or skins after the alkali swellingprocess from a pH of above 12 down to a pH of from 7 to about 8, as forexample with such neutralizing agents as sodium bicarbonate and boricacid.

This neutralizing operation was quite disad- 10 vantageous in manyrespects. It tended to shrink the extended fibres quite rapidly andapparently tended to shorten them irreversibly, with the result thatafter tanning a fiat piece of leather was formed. 5 Moreover, theneutralizing reaction tended to break up the soaps and emulsions orcolloidal solutions of fats or greases, with the result that these fatsor greases or free fatty acids formed by hydrolysis were precipitatedupon and/or ab- 9 sorbed by the surface of the hide or skin. Thisinclusion of a relatively impervious layer of fatty, greasy, and/r waxymaterials over the surface of the skins or hides often interfered withthe uniform action of the enzyme preparation during the unhairingprocess, but in addition made it impossible to remove readily the fats,greases, and waxes contained in the skins or hides.

In order to obtain a good and uniform piece of leather, particularly ofa uniform color without mottling or spotting, and/or with a uniform ap-5 plication of finish,'it was necessary subsequently to degrease theskins or hides, as for example with acetone and benzene, as otherwisethe subsequent processes would tend to take place irregularly. Inaddition the skin or hide would 10 tend to spew, resulting in the greaseor fat gradually working itself to the surface and spoiling theappearance thereof.

An object of the present invention is to provide an enzymatic dehairingprocess for skins or hides, in which it will not be necessary to causesubstantial neutralization of the skin or hide after preliminaryalkalization treatments, and in which assurance will be had that thegreases, oils and fats and relatively insoluble soap combinations willnot be precipitated upon the skin or hide previous to the unhairing,bating, tanning, and other treating processes.

Another object is to provide an enzymatic treatment for hides or skinsin the preparation of leather in which the preliminary alkalizationtreatment may be substantially directly followed .by the enzymaticdehairing treatment without a substantial neutralization operation orwith only relatively slight neutralization of the skin or hide afteralkalization, such neutralization being insufficient to cause depositionof greasy, waxy and/or fatty materials upon the surface of the leather.

Other objects will appear during the course of the followingspecification.

It has been found according to the present mvention that it is possibleto eliminate the customary neutralization process, which reduces the pHof the hide or skin after alkalization from about above 12 to about 7 to8. According to the present invention, on the other hand, the alkalizedskin or hide is subjected without substantial neutralization to anenzymatic dehairing process after it has been only slightly modified byreducing the pH to between 11 and 9 or preferably from about 12 to about9.6.

The present invention contemplates the dehairing of hides or skins underpH conditions much higher than heretofore contemplated in whichconnection certain enzymes may be most effectively employed. Among theproteolytic enzyme preparations which may be most satisfactorilyemployed are those which are derived by the growth of certain bacteriaunder specified conditions, said enzyme preparations being mostdesirably employed in a mixture containing carbohydrate and proteindecomposition products which mixture tralized to a pH of between 7.5 to9.5 and preferably about 8.5 and it is then sterilized, as for example;with steam under pressure and 140 C. for 35 minutes. 1

After the liquor has been sterilized and its pH has been reduced toabout 6.2, it is inoculated with a pure culture of the bacillus of themesentericus or subtilis families. The culture is allowed to develop ator about room temperature or slightly thereabove, and in one instance atemperature of 30 to 40 degrees C. was found most satisfactory.

' the subsequent enzymatic processes. 76

While "the culture is developed it is preferably kept in relatively.thin layers not exceeding onehalf of one inch thickness and iscontinuously supplied with sterile air which has free access thereto.

- After the culture has suitably developed and suflicient of theenzymatic product and metabolic carbohydrate and protein decompositionproducts have been formed ,in the liquor, a suitable disinfectant shouldbe added to stop further bacterial growth and to devoid the liquor ofliving microorganisms.

The antiseptic must be most carefully regulated so as not todisadvantageously affect the relatively delicate enzymatic productsformed and at the same time must be controlled so that it will assurethat there will be no living bacteria present nor any livingmicro-organisms, as otherwise the subsequent dehairing process would beunsatisfactory. Among the preferred antiseptics which may be employedpreferably in combination are phenol, cresylic acid, betanaphthol, andotherphenol derivatives and preferably consisting of the hydroxylatedcompounds-of monoalkylated or polyalkylated benzenesor of naphthalenes,which may also be halogenated or chlorinated.

Preferably these disinfectants are utilized in combination, as, forexample, in combination of pine oil and naphthol or naphthol andcresylic acid, or cresylic acid and pine oil, or all three, since thecompounds in combination appear to be more satisfactory than any ofthese antiseptics when utilized alone. Preferably the antiseptic isadded to the mixture in amount of-much less than 2%, and preferably inamounts less than 1% with a preferred range of between 0.5v to 0.75%.

The enzymatic medium then which is preferably filtered from insolublematerials contains the proteolytic enzymatic composition and usuallydesirably also amylolytic and lypolytic enzymes, and in additionmetabolic decomposition products of the proteins and carbohydrates,particularly various hexoses, polysaccharides, dextrines, amino acids,peptones, albuminoids, and so forth.

These protein decomposition products and particularly the amino acidsappear to have a most advantageous action on the dehairing process inThis enzyme composition may be most satisfactorily utilized with hidesor skins which have been prepared as previously stated by alkaliz'awillbe subsequently above 9 and say between 10 I and '11.-

The process of present application is particularly adapted tolightweight skins, such as kidskins, goatskins, sheepskins, calfskinsand so forth.

In preparing these hides or skins for treatment with the enzyme, it hasbeen found most satisfactory to treat them with caustic alkali solutionsranging from 0.01 to 1.0 normal concentration with a preferredconcentration at about 0.10 or between 0.05 to 0.3 normal. The preferredtemperature range is from 20 to 40 degrees and it may approximate about30 degrees.

In one procedure about 100 parts by weight of skins or hides were placedin a bath containing 800 parts by weight of water and 4% to 6 parts ofcaustic soda, a sodium hydroxide between N/8 and N/10 being mostpreferably employed. The temperature of the bath at the commencement ofthe reaction was maintained at about 86 F. and it was gradually allowedto fall to about 70 F.

The treatment with alkali preferably takes place with agitation orstirring and may be conveniently performed for a period ranging from 12hours to 96 hours with a preferred range from 1 to 3 days. After thistreatment the hides will have a pH of 11 to 12 or above and in onepreferred procedure it is desirable to reduce their pH to between about10 to 11 or to between about 9.6 and 11.

In reducing the alkalinity of the skins or hides it has been found mostsuitable to cause a gradual reduction, as for example, bywashing withwater, preferably without the utilization of sodium bicarbonate or boricacid in such quantities. It is not preferred that a reduction to between7 to 9 in the pH value should be caused with the many disadvantageouseffects above described.

According to one procedure, in accordance with the present application,100 pounds of dried goat skins are soaked two days and are thenpreferably broken and fleshed. These goat skins are then subjected to adilute caustic soda solution in a paddling apparatus. This paddlingapparatus may be of 950 gallons capacity and contain in solution 41 A;pounds of caustic soda. It has been vfound desirable in this causticsoda treatment to also have present a neutral salt, as for example, 41%pounds of some neutral alkali metal salt, as sodium chloride or sodiumsulphate.

In one instance about 2 parts of sodium sulphate were utilized for aboutevery one part of .soda to prepare a suitablealkalizing bath.

The goat skins were treated in this paddle with alternate agitation andrest periods, with the "rest periods increasing and the agitationperiods After this washing to slightly reduce the sir of the skins orhides to between 9.6 and 11, these pending upon the amount of time whichintervenes before the enzymatic treatment the washing period may bevaried. For example, if the skins or hides are ready for treatment withthe v enzymatic liquor prepared as stated above. .De-

skins are to be'subjected to enzymatic treatment but if they are to besubjected the next day they need be washed only for 40 to 45 minutes. Onthe other handif they are to be subjected to the enzymatic treatment twodays later, they are washed for only twenty minutes. After the washingprocess the skins are preferably treated with an alkali material ofsubstantially less alkalinity than caustic, as for example borax.

In the present instance it has been found satisfactory to add from 4 to8 pounds of borax to 500-900 pounds of the skins in the paddle and thento alternately paddle and permit the skins to rest while maintaining apH of the solution between 10 and 11. After this borax treatment theskins or hides may be directly subjected to the enzymatic treatment, theenzymatic liquor being added to the paddle. For example, the thirtypounds of the enzymatic liquor may be added to the paddle together withammonium chloride, sodium bisulphite and a small amount of boric acid.In one instance from six to ten pounds of boric acid, from two to tenpounds of ammonium chloride, and from 1 to thirty pounds of thebacterial enzymatic liquor were utilized. The pH of the skin or hide atthis time was substantially above 8 and preferably above 9.

To this enzymatic liquor during the unhairing process may beconveniently added some of the disinfectant solution, as mentionedabove. After the unhairing treatment has been completed, the enzymaticliquor is removed, the skins are washed and some disinfectant is addedto the paddle as above described. After unhairing the skin and hides arethenpreferably washed, most desirably with a wash water having a pH ofabove 9 and preferably between 10 and 11. This alkaline washing has theeffect of cleansing the skins and hides.

1 The skins and hides may then be bated with a high degree ofsatisfaction. This hating process, of course, may be followed by theother leather manufacturing process including tanning.

By maintaining a relatively high pH during the unhairing process, asabove described, and also by utilizing specially prepared enzymes, whichare most satisfactorily employed undersuch conditions, a mostsatisfactory unhairing process is obtained with a production of a moredesirable grade of leather of higher quality.

In addition to or in lieu of the bacterial enzymes preferred employed,may also be utilized proteolytic enzyme preparations containingpancreatin, papain, trypsin, bromelin, and enzyme mixtures orcompositions derived from Aspergillus oryzae, niger and/or Penicillium,Mucor delemar, amylomycesrouxii, Tryotria: tennis and so forth.

What is claimed is: I

1. A process of dehairing skins and hides which comprises subjectingthem to successive treatments with a caustic alkali solution and with anaqueous solution of a bacterial proteolytic enzyme at a pH substantiallyabove 8.0, said successive treatments being carried out withoutintervention of an intermediate treatment with a solution of sodiumbicarbonate.

2. A process of dehairing skins and hides which comprises subjectingthem to successive treatments with a' caustic alkali solution and withan aqueous solution of a proteolytic enzyme derived from bacterialgrowth, said last treatment being carried out under sterile and highlyalkaline conditions, said successive treatments being carried outwithout intervention of an intermediate treatment with a solution ofsodium bicarbonate.

3. A process of dehairing skins and hides'which comprises subjectingthem to successive treatments with a caustic alkali solution and with anaqueous solution of a bacterial proteolytic enzyme at a pH between 8 and11, said successive treatments being carried out without intervention ofan intermediate treatment with a solution of sodium bicarbonate.

4. A process of dehairing skins and hides which comprises subjectingthem to successive treatments with a caustic alkali solution and with anaqueous solution of a bacterial proteolytic enzyme in presence ofmetabolic amino derivatives at a pH of above 9, said successivetreatments being carried out without intervention of an intermediatetreatment with a solution of sodium bicarbonate.

5. A process of dehairing skins and hides which comprises subjectingthem to successive treatments with a caustic alkali solution and with anaqueous solution of a sterile bacterial liquor de-

